Method: A thrombin time (TT)-dabigatran concentration curve was calculated using dabigatran plasma calibrators (Aniara, West Chester, OH). The effect of dabigatran on activated partial thromboplastin time (aPTT) was also calculated. A table of dabigatran concentration, TT and aPTT was produced and distributed to all stroke team members. A protocol was developed, in which a dabigatran concentration of <47 ng/ml (corresponding to a TT <19.7 s and aPTT <37 s) was selected as the upper limit for safe thrombolysis. In tertiary stroke centres, a TT and aPTT were both ordered, while in peripheral telestroke centres, the aPTT alone was used to determine dabigatran activity.

Results: In the 4 months since development of the protocol, eight potential thrombolysis candidates taking dabigatran were assessed with CT at a median (IQR) time of 192 (143) minutes. The median NIHSS was 16 (12). Based on TT/aPTT, only 2 patients were ineligible for thrombolysis (dabigatran concentrations >118 ng/ml). Another three patients were not treated due to minor/resolving symptoms and a fourth due to intracerebral hemorrhage. Two patients were treated with intravenous tPA (0.9 mg/kg). A repeat CT head at 24 hours revealed no hemorrhagic transformation in one patient and asymptomatic petechial hemorrhagic transformation (European Cooperative Acute Stroke Study Grade Hemorrhagic Infarction Type 1) in the other.

Conclusion: It is possible to safely administer intravenous tPA in dabigatran treated patients, provided a reliable method of measuring anticoagulant activity is available. Although, TT and aPTT dabigatran concentrations do vary between laboratories, individual protocols can and should be developed at acute stroke treatment centres.